1. Field of the Invention
The present invention relates to a technique for reading out a data signal from a memory unit and driving a functional device.
2. Description of the Related Art
Reference is made to a printer, as a popular example of reading out a data signal temporarily stored in a memory unit and driving a functional device. FIG. 26 is a block diagram showing a constitution of a popular printer provided with a semiconductor device for temporarily storing and reading out an electric signal.
FIG. 26 specifically shows a functional block diagram of a conventional inkjet printer for recording a letter or an image by firing a minute droplet of ink such that the ink droplet flies and sticks onto a recording medium such as a paper sheet.
The inkjet printer is provided with a main body including a substrate 105 and a printhead 100 installed therein. The printhead 100 is provided with a driving circuit 101, an ink tank 102 and an injector 103. The substrate 105 comprises a memory unit 106 and a data signal providing unit 104.
Ink liquid is supplied from the ink tank 102 to the injector 103 through a prescribed flow path. A driving signal for activating the injector 103 is generated at the driving circuit 101 when a data signal output from the data signal providing unit 104 is input to the driving circuit 101, and input to the injector 103. Upon receipt of the driving signal the injector 103 fires an ink droplet. A conventional inkjet printer is provided with a plurality of nozzles for firing the ink droplets, but printing quality may sometimes deteriorate because of uneven performance of the nozzles resulting from a manufacturing fault etc. For preventing this problem a conventional inkjet printer is designed to perform a firing operation so called a “multi-pass mode”.
The multi-pass printing operation shall be described referring to FIGS. 27 and 28. FIGS. 27 and 28 respectively show an example of a multi-pass printing operation. Referring to FIG. 27, the printhead 100 repeats firing actions while moving in a rightward direction from a start position 111. In this case, during a rightward motion and a leftward motion respectively, the printhead 100 fires ink droplets either to an identical point or to a different point shifted by a predetermined distance, over a portion indicated as a multi-pass printing region 110. When the printhead 100 reaches an end position 112 it moves downward to a transition position 113. Then the printhead 100 repeats firing actions moving in a leftward direction. Meanwhile referring to FIG. 28, the printhead 100 repeats firing actions moving back and forth over the multi-pass printing region 110 until it reaches the transition position 113, after which the printhead 100 repeats similar actions. In both of these cases, ink droplets fired from different nozzles fall on an identical point in the multi-pass printing region 110, therefore even if uneven injection is caused in the injector 103 the unevenness can be leveled off and corrected by overlapping the ink droplets or placing the ink droplets with a certain shift.
For performing such multi-pass operation, the memory unit 106 of a conventional inkjet printer shown in FIG. 26 stores at least a data signal necessary for printing on the multi-pass region 110. Generally, data in the memory unit 106 is read out by inputting an address signal to the memory unit 106 from a host device (not shown). Here, the address signal stands for a signal that serves for designating a memory cell stored in the memory unit 106 in a form of a matrix array, which signal may designate either a single memory cell or a plurality of memory cells, and further be a combination of an address signal of a leading memory cell and a signal indicating a number of the memory cells, therefore address signals in accordance with a system constituting the memory unit 106 shall be herein referred to as an address signal as a whole. The data signal read out from the memory unit 106 is transmitted to the driving circuit 101 on the printhead 100 through the data signal providing unit 104, and transmitted from the driving circuit to the injector 103, so that the injector 103 performs a firing action in response to an instruction of the driving circuit 101. This operation is repeated until firing actions for the entire multi-pass region are completed.
These days there is a growing demand in the field of inkjet printer for a higher speed printing performance and higher print quality. In order to fulfill such requirements, remedies such as increasing a number of nozzles or operating frequency of a printhead must be taken. Since such measures naturally lead to an increase of data signals for printing, performance level of circuits on the substrate 105 in the printer main body or the driving circuit 101 of the printhead 100 etc. in FIG. 26 has to be upgraded. Also, with an increase of a number of nozzles some measures must be taken for preventing variation of ink droplet volume to be fired from each of the nozzles. For these reasons the correction is executed by the multi-pass printing, to achieve a high quality print by an inkjet printer. However, in case where the multi-pass printing is to be performed on a conventional printer as shown in FIG. 26, identical data signals have to be transmitted over a plurality of times from the memory unit 106 through the data signal providing unit to the driving circuit 101, which inevitably results in an increase of power consumption and a higher cost of the printer, in exchange with a quicker operation and higher quality of its printing job.
The foregoing problem is not limited to an inkjet printer, but is common to other semiconductor devices in which a data signal read out from a memory unit, or another signal generated based on such data signal is to drive an active element, and besides the same data signal is repeatedly required for each driving cycle. In such a case accordingly, a similar problem to the case of the inkjet printer arises as a result of a quicker action or higher performance level of a semiconductor device. Specifically, an increase of operation frequency leads to increased power consumption, or achieving a higher performance of the data signal providing unit 104 results in a cost increase.
The invention has been made in view of the foregoing situation, with an object to restrain an increase of power consumption of a semiconductor device. It is another object of the invention to restrain a cost increase due to upgrading a performance level of a semiconductor device. Also, it is another object of the invention to restrain a power consumption increase arising from upgrading a performance level of a printer. It is still another object of the invention to restrain a cost increase due to upgrading a performance level of an image output device.